A: The euphoria that some people report from exercise is often referred to as a "runner's high," though it's been linked with a range of other activities, from swimming to biking to grueling workouts at the gym.

But the phenomenon is not well understood. Some people appear to experience full-blown runner's highs from very intense bouts of exertion — such as running a marathon or finishing a miles-long bike race — and others from less-taxing workouts. Some people liken a runner's high to that from cocaine or other street drugs, while others say exercise makes them feel very good but not ecstatic.

How long it takes for an all-out runner's high to kick in — if it does — seems variable, but it's generally associated with prolonged bouts of exhaustive activity. Even with that level of exertion, though, there are no guarantees you'll be flying high afterward.

"There is a runner’s high but most people really do not get it," says Dr. John Ratey, a psychiatrist at Harvard Medical School and author of the forthcoming book "Spark: The Revolutionary New Science of Exercise and the Brain," due out in January.

Still, muscle soreness aside, most of us do feel better from exercising, even if we don't actually feel over-the-top euphoric, Ratey notes.

"Almost everyone gets a boost in mood and usually fairly quickly," he says.

Studies have shown that one 30-minute session of moderate-intensity exercise can help ease distress, depression, tension and anger, says Michael Bracko, an exercise physiologist in Calgary, Alberta, Canada, and a spokesperson for the American College of Sports Medicine.

Exercise appears to raise levels of various chemicals that help boost our mood.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

It was long thought that a runner's high resulted exclusively from the release of feel-good chemicals known as endorphins. Back in the 1970s, researchers found elevated levels of endorphins in runners' blood. But those endorphins don't actually make their way into the brain to exert an effect, Ratey explains. Instead, researchers now believe, the mood-boosting effects of exercise may be the result of increases in the brain itself of endorphins as well as several other chemicals including serotonin, dopamine and norepinephrine.

Being active feels good for other reasons, too. For one, you're doing something good for your body. You're overcoming inertia, and that can be a huge boost and an important step forward for couch potatoes wanting to shed some pounds.

There's also the sheer enjoyment that many people feel from participating in a sport or other activity they love.

Plus, if you're tired and have been stuck in an office all day, a simple 10-minute walk around the block offers a change of scenery and some fresh air that can give you a much needed pick-me-up, Bracko says.

Bottom line: You don't have to run marathons to feel good from physical activity.

Q: I am working on losing 50 pounds and I would like to know what the best exercises are for keeping my breasts firm. A few of my female friends dropped a lot of weight and experienced sagging in their chest. What do you recommend?

A: While there aren't any exercises for your actual breasts, you can keep the underlying chest muscles strong and firm with strength-training activities such as the bench press and chest fly.

These moves can be done with machines or free weights, and trainers commonly recommend doing one to three sets of eight to 12 repetitions at a weight that fully fatigues your muscles by the last repetition.

Another tip: Invest in a good sports bra to minimize bounce and stretching during physical activity.
A recent British study
found that breasts can move up and down as much as 8 inches during exercise — ouch! That's a workout for your breasts, all right, but no good will come of it.